Breast Tissue Assessments Based on High Order Mechanical Properties

Summary

Ultrasonic tissue elasticity imaging, which can visualize diseased tissues based on their stiffness, is a useful technique for breast cancer detection. In general, soft tissues including the breast have nonlinear elasticity and viscoelasticity referred to as high order mechanical properties. These properties make the conventional elasticity evaluations based on strain and Young’s modulus images difficult because these images vary depending on various conditions, in which high order mechanical properties cannot be neglected. For mechanical assessment independent of such conditions, high order mechanical properties must be assessed. Moreover, these properties also change in diseased tissues. Therefore, in this chapter, a method to assess high order mechanical properties is proposed with the aim of improvement of diagnostic ability. In actual breast assessment, cyclic loading and unloading were applied to the body surface by freehand manipulation of an ultrasonic probe; then, the nonlinear elasticity and viscoelastic hysteresis parameters were estimated and visualized based on the surface pressure measured with the pressure sensor, and the local strain distribution was estimated by the combined autocorrelation method. Nonlinear elasticity and hysteresis parameters, which can be estimated by the proposed method, clearly discriminated the breast tumor from the surrounding normal tissue.